<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>事件流</title>
	<style type="text/css">
	#content{width: 150px;height: 150px;background-color: red;}
	#btn{width: 80px;height: 80px;background-color: gray;}
</style>
</head>
<body>
	<div id="content">content
		<div id="btn">button</div>
	</div>

	<script type="text/javascript">
		var content = document.getElementById("content");
		var btn = document.getElementById('btn');
		btn.onclick = function(){
			alert("btn");
		};
		content.onclick = function(){
			alert("content");
		};
		document.onclick = function(){
			alert("document");
		}
	</script>
</body>
</html>